The heart has four chambers, the right and left atria and the right and left ventricles. The atria serve as primer pumps to the ventricles which in turn pump blood to the lungs (the right ventricle) or the aorta and the remainder of the body (the left ventricle). The heart is essentially and electromechanical pump, which contracts and pumps blood by means of a wave of depolarization that spreads from the atria to the ventricles in a timed fashion through a series of conduction pathways. Cardiac arrhythmia is a condition afflicting the heart and is characterized by abnormal conduction patterns which in turn can affect the pumping efficiency in one of more chambers of the heart. It can occur in either the atria, ventricles or both. Particular types of Atrial arrhythmia can cause a condition known as atria fibrillation (AF) in which the pumping efficiency of the atria are compromised. Instead of contracting in a coordinated fashion, the left or right atria flutter with little or no pumping efficiency.
During an episode of AF, the normal electrical impulses that are generated by the sin θ-atrial node (the SA node), the natural pacemaker of the heart are overwhelmed by disorganized electrical impulses, known as ectopic foci that may originate in the atria or pulmonary veins, leading to conduction of irregular impulses to the atria and the ventricles. This can result in an irregular heartbeat, known as an arrhythmia which may occur in episodes lasting from minutes to weeks, or years. Left unchecked, AF often progresses to become a chronic condition.
Atrial fibrillation is often asymptomatic, and while not immediately life-threatening, may result in palpitations, fainting, chest pain (angina), or congestive heart failure. Patients with AF have a significantly increased risk of stroke and pulmonary embolism due to the tendency of blood to pool and form clots or emboli in the poorly contracting atria which are then sent to the lungs in the case of the right atria causing pulmonary embolism, or the brain causing stroke.
Atrial fibrillation may be treated with medications, implanted ventricular defibrillators or surgical procedures. The current medications used either slow the heart rate or revert the heart rhythm back to normal. However patients must remain on medication for life and many patients cannot be successfully treated with medication. Implanted ventricular defibrillators may be used to deliver a series of high voltage electric shocks to convert AF to a normal heart rhythm in a technique known as synchronized electrical cardioversion. However, these shocks are extremely painful and may cause the patient to pass or literally be knocked to the ground from the shock. Surgical and catheter-based therapies may also be used to ablate or destroy portions of the atria and pulmonary veins containing the ectopic and other foci responsible for the generation of arrhythmias causing AF; however these require open heart surgery, cardiac catheterization or both and have met with limited success. Thus, there is a need for improved methods and devices for the treatment of atrial fibrillation.